Retrospective study of preventive effect of maize on mortality from Parkinson's disease in Japan.

The findings of a negative association between past maize (Zea mays) production and current Parkinson's disease mortality by each prefecture in Japan tends to support the hypothesis that the nutritional condition that causes niacin deficiency might protect people from Parkinson's disease. Specifically, the negative association between both the area planted for dried corn in 1960, 1970 or 1977 and the area planted for sweet corn in 1960 and age-adjusted death rates for Parkinson's disease is ecological evidence supporting the hypothesis. Extending the analysis to other cultivated crops, even stronger negative associations of age-adjusted death rates for Parkinson's disease and cultivation of rice and soybeans were found, but associations were not significant for a large variety of vegetables. The findings for soybean and rice are attributed to the correspondence (co-linearity) of cultivation of these other two seed-crops with maize. Hence, further testing of the theory of niacin deprivation and prevention of Parkinson's disease finds some circumstantial support in the cultivation patterns of a grain of poor niacin and tryptophan availability.